1. Field of Invention
This invention provides a safe means and method for protecting customer""s grounding electrode conductors from electric utility ground and open neutral fault currents.
2. Description of Prior Art
Prior art is fully described in the National Electrical Code. The National Electrical Code does not provide an overcurrent protective device for grounding electrode conductors. The Grounding electrode conductors are connected directly from the grounding electrode to the neutral.
Ground faults and/or open neutrals on the electric utility""s system, on the line side of the customer""s main service, and on customer""s electrical equipment have resulted in an overcurrent protective device for grounding electrode conductors. The grounding electrode conductors are connected directly from the grounding electrode to the neutral.
Ground faults and/or open neutrals on the electric utility""s system, on the line side of the customer""s main service, and on customer""s electrical equipment have resulted in fault currents returning to the system neutral via the (1) earth, (2) grounding electrode, and (3) grounding electrode conductor. Many times these currents are sufficiently large enough to overheat and even melt the grounding electrode conductor and/or neutral conductor. Fires have resulted from the overheating and/or melting of the grounding electrode conductor and/or neutral conductor. Prior art has not prevented these fires and provides no absolute method for positively preventing these fires.
In prior art, the electric utility system""s or customer""s overcurrent protective devices were relied upon to sense the fault and clear it. However, the settings and sizes of overcurrent devices of the utility""s system are set to protect the utility""s system equipment only. When setting or selecting these overcurrent devices, no consideration is given to protecting the customers grounding electrode conductor from overcurrents due to utility system ground faults or open neutrals.
The electric utility""s neutrals most often have ampacities larger than the ampacity of a No. 6 copper wire, the most common size of the grounding electrode conductors of customers. To provide the required customer load, the electric utility, in most cases cannot size their overcurrent protective devices small enough to prevent overcurrents on the customer""s grounding electrode conductor or neutral conductor.
Likewise, grounding electrode conductors on customer transformers and services are not protected by overcurrent protection on the grounding electrode conductors. Feeder and branch circuit breakers are not sized to prevent overcurrents on grounding electrode conductors at transformers and services.
In accordance with the present invention an overcurrent device is installed between the neutral and the grounding electrode conductor at the service equipment and at the first overcurrent protection downstream of transformers.
Accordingly besides the objects and advantages of the method of overcurrent protection described in my above patent, several objects and advantages of the present invention are:
(a) to provide a superior method to protect electric utility customer""s grounding electrode conductors from overcurrents resulting from electric utility ground faults and open neutrals;
(b) to provide a superior method to protect grounding electrode conductors from overcurrents resulting from ground faults and open neutrals on the customer""s service entrance conductors and equipment on the line side of the service equipment;
(c) to prevent fires due to overcurrents on grounding electrode conductors;
(d) to prevent the loss of property and lives from fires originating from overcurrents on grounding electrode conductors;
(e) to provide a method of overcurrent protection which is safe when the overcurrent protection device trips; and
(f) to provide an additional level of safety from ground faults.
Further objects and advantages are to provide a positive method of overcurrent protection of grounding electrode conductors which can be used easily and is inexpensive to manufacture in various ampere ratings to achieve the required protection. Still further objects and advantages will become apparent from a consideration of the following description and drawings.